I pass through DTX fairly regularly and shop/eat there from time to time. I have friends in some of the luxury buildings there as well and have a habit of walking around late at night rather than taking cars, so I've seen it all at different times. The thing about "Downtown" is that it's like 4 micro neighborhoods.
1. Summer/Winter corridor between Tremont and, say, Devonshire (including part of the Ladder Streets and Tremont fronting the Common)
2. Theater district, on Washington from Boylston to West St (also including part of the Ladder Streets)
3. Pure financial district with the epicenter around Post Office Square reaching out to the greenway east-ish
4. Government Center limited by the backside of Beacon Hill/West End and encompassing Quincy Market and Faneuil Hall
(3) is super quiet outside of peak business hours and (4) is either dead or full of tourists depending on the weather. (2) ebbs and flows with theater shows, AMC movie times, and a few great bars on West and Temple. (1) is clearly the area with the most "issues" especially if you include Washington 1 block on either side of its intersection with Summer/Winter. I'd have no worries walking through (3) at 4AM, while I miiiight think twice about strolling through (1).
All 4 of these regions need more restaurants and bars, but they particularly need housing so that there's a steady flow of people and not just peak-trough waves of visitors tied to shows and the 8 hour workday 3 days per week.
To your specific questions, things are absolutely better than the low point of the pandemic. It was outright spooky where the streets would be just 3 guys in wheelchairs, pushing themselves backwards down Washington Street. There are too many vacancies and the little movement there is (WNDR museum, some outdoor seasonal programming) doesn't seem to move the needle much. Roche Brothers is a staple as is the Macy's, and things would get much much worse if either of those closed. An anchor tenant restaurant back in the Millennium Tower would also be a godsend since Pabu closed during the pandemic.
My optimistic brain sees some green shoots, particularly around Temple Place where there's a great run of bars, restaurants, and cafes, with a few more on the way. George Howell (technically on Washington), JM Curley's/Bogies/Wig Shop, Cafe Bonjour, Democracy Brewing, Hobgoblin, and an upcoming trio of new spots from Jamie Bissonette will do a ton to anchor that particular stretch, especially since they stay open late. There were plans for two infill hotels on blocks just off Tremont, one of which is approved I think, but I haven't seen any sign of construction. Hopefully the new Holocaust museum just down from the Statehouse will also do something to move some of the stickier characters off the block.
It's a lot, I know, but Boston is lucky to be quite safe and never feel totally hollowed out (other than ~Apr-May 2020). Recovery takes a long time, so hoping we don't have backsliding in the coming years.